This invention relates generally to truss boom structures, and more specifically, to long lightweight deployable truss boom structures. Many space missions require the use of long lightweight deployable truss booms. Truss booms have been used extensively in spacecraft as masts to support and accurately position a feed-horn for a large antenna or to deploy and tension the blankets of a solar array. Common boom applications are for deployment and support from spacecraft of items such as scientific instruments, cameras, solar arrays, antennas, sun shades, optical components, magnetometers and “gravity gradient” masses which stabilize satellites in their attitude toward earth. Recent missions carrying truss booms have been the Mars Pathfinder, Cassini and the Lunar Prospector. Truss booms have been flown in lengths as long as the 60 meter boom which was utilized for the Shuttle Radar Topographic Mission of September, 1999.
A pervasive problem with conventional truss booms is that the length of their deployed or elongated configuration makes the truss boom almost impossible to transport in that configuration. For land-based applications the solution is quite simple. The truss boom is provided as a group of individual parts which are joined together at the site. However, for space-borne equipment this solution is not appropriate. To overcome this problem, numerous arrangements have been proposed for storage and transport of truss booms in a retracted configuration, which occupies a relatively small volume and has a much reduced axial length. Stowed truss booms are released from their retracted configuration and caused to extend to their deployed configuration. This available change in bulk volume and axial length enables a long truss boom to be carried in a small cannister, and to be deployed only when needed.
There are two primary types of conventional stowable truss booms: (1) helically coilable booms having continuous longerons such as the coilable boom manufactured by AEC-Able Engineering Co., Inc., Goleta, Calif. and (2) articulated truss booms having segmented longerons such as the ADAM articulated mast manufactured by AEC-Able Engineering Co., Inc., Goleta, Calif. Helically coilable truss booms are composed of longerons which are extremely thin and flexible, and they are stowed by helically coiling the truss boom inside a storage cannister. Segmented truss booms are composed of segmented longerons which are discontinuous at each intersection between the longerons and connecting battens. They are stowed by stacking the segmented longerons and battens within a storage cannister. Both types of conventional truss booms stow for launch by coiling or folding inside a storage canister which has a length of about 2.3% of the deployed length of the truss boom. Thus, a sixty meter truss boom would require a storage cannister which is 1.4 meters long.
Present space missions require longer truss booms, however, the maximum length of presently available truss booms is limited to about sixty meters. The limitations of the maximum length of truss booms include their required stowage area and their weight, both attributable in part to the requirement for a storage canister. As coilable truss booms are helically wound inside of a storage cannister for stowage and transport, coilable truss booms generally utilize thin longerons of low modulus material resulting in low boom stiffness and a long undesirably flexible deployed truss boom. As articulated truss booms are transported as segments of a manageable length for stowage and transport, deployment of the truss boom requires the segments to be connected together at connection joints, and slippage at these connection joints is a drawback which this type of boom may experience.
FIG. 1 illustrates a conventional truss boom 10 structure composed of load carrying axial longerons 12 that are stiffened by stabilized by battens 14 and diagonals 16. The truss boom 10 is utilized to support a feed horn of an antenna 18. The truss boom 10 is stowed inside of a storage canister 20. As shown in FIG. 1, another major limitation with conventional stowable truss booms 10 is that there is no room within the storage canister 20 for apparatus such as instrumentation or control devices. Such apparatus, for example an antenna 18, must be attached to the leading end of the truss boom 10 and stowed exterior to the storage cannister 20.
The object of the present invention is to provide a truss boom which is much longer in length upon deployment than presently available truss booms. The truss boom must be capable of compact stowage within the confines of a spacecraft, and it must be deployable in space.